How many hours can an employer force you to work?

Can an employer make you work continuously for long periods of time with only the minimum breaks, and for how long? If we go by the maximum 48 hours a week which they can force you to do unless you agree to do more, can they make you work 4 x 12 hour shifts in 4 days? Or even 3x 16 hour shifts!? I mean...where does it all end? If you, as the employee speak up and say that you do not want to work so many hours at a time, can you be sacked?

I'd love to work 3 x 16 hour shifts! 48 hours pay but with 4 days off per week sounds just great to me!

(Back in my student days I worked 7 x 16 hour shifts for 10 weeks in a row. 112 hours per week certainly helped my bank balance! I've also worked 24 hours on, 12 hours off for long periods).

However the current regulations make working three 16 hours shifts on successive days, at the same times an illegal employment practice because of the requirement to have 11 hours rest between the end of one working day and the start of another. However three 16 hour shifts in a week is not illegal, per se, as long as the shifts are spaced far enough apart to provide 11 hour rest breaks. The rules on night-working might also be relevant.

Chris' answer is (as always) the correct interpretation of the Working Time Directive. However that is the statutory position - what the law says the employer must or mustn't do.
However you are not legally obliged to work more than your contracted hours - so if your contract says you will work 37 hours, that's all you HAVE to do.
Now, a couple of issues with that.
1) In these uncertain times, some employers put-upon employees to work more, with a (unsaid) threat of 'you'll be dismissed if you don't'. Only you can judge the likely probability of that.
2) You may be on a zero hours contract. These work 2 ways - the employer isn't obliged to offer you work, and if offered, you aren't obliged to take all of it. But now refer back to point 1).

The reason for things like the working time directive is to protect the health of employees - who cannot simply leave especially in this economic climate and need protection from exploitative and unscupulous employers.

If you don't like it tamborine i suggest you leave - plenty of opportunities to set up sweat shops in the far East I hear

Contrated hours are 30 a week and being rotered to work 48 hours, sometimes slightly more even though not agreed to it. Also, quite often they are breaking the rules and giving me less than 11 hours rest between breaks.

Whoever says that the days of slave labour are gone is smoking crack.
It is easy to say so when you are not being pressured and bullied by your employer into dropping everything for the sake of work and being given excessive hours with skipped breaks and few hours of break in between shifts.

Perhaps the office workers who get to work 9-5 with perhaps a few hours of overtime each week sitting by their desk are fortunate enough to be able to judge and look down upon the rest of us.

As for "If you dont like it then leave!" remarks from certain people...well, that is not easy to do when you have no job lined up and not enough time or energy to be looking for for a new one whilst being exploited in your current one.
So let's not hear anymore ignorant comments like:
" Plenty of people would love to be doing your job. Stop being lazy!"

Statutory rules on breaks are here. http://www.direct.gov.uk/en/Employment/Employe es/WorkingHoursAndTimeOff/DG_10029451
Then look at the linked page on employers' health and safety responsibilities - particularly the section at the bottom caled 'What to do next'.
Probably not go in guns blazing with 'you're not allowed to roster me like this under the WT Directive'. Perhaps better to approach it with 'look I'm really committed to this company and the job but I'm finding the gaps between the breaks rather short - is there anything we could do about it? Follow that with 'what are the legal minimums for this?'
Try and find out whether they are mere ignoramouses or simply out to exploit people whatever. At the end of the day, you can report them to the Health & safety Executive.